A thermal printer known in the past conveys a print medium such as thermal recording paper to a contact position between a thermal head, in which heat generating elements are linearly disposed, and a platen roller arranged to be opposed to the thermal head and controls energy applied to the thermal head to, for example, cause the print medium to develop a color to thereby form a print pattern on the print medium.
When a large number of places where the thermal head should be simultaneously heated are present on one line of print data, in some cases, power consumption increases to exceed the capacity of a power supply that supplies electric power to the thermal printer. In such a case, an inconvenience occurs in that a desired print result cannot be obtained because the energy applied to the thermal head runs short and print is blurred or conveying speed of the print medium falls.
As a related art for solving such a problem, a thermal printer disclosed in JP-A-5-77469 is known. The thermal printer is configured to appropriately adjust, in order to perform printing while keeping power consumption within a limit of a power capacity, energy applied to a thermal head and conveying speed of a conveying unit configured to convey a print medium.
However, depending on print data, power shortage still occurs even if the energy applied to the thermal head and the conveying speed of the conveying unit are adjusted as in the thermal printer disclosed in JP-A-5-77469.
When a large number of sheets are printed, extremely long time is required until completion of the printing if conveying speed of a print medium is set low.
Among thermal printers, some thermal printers include a thermal head configured to perform printing on the rear side of a print medium in addition to a thermal head configured to perform printing on the front side of the print medium and simultaneously perform printing on both the front side and the rear side of the print medium. When the printing is simultaneously performed on both the sides of the print medium, a large amount of power is necessary compared with printing performed only on one side of the print medium. Therefore, the problem of the power shortage is more conspicuous.